Generally, the characteristics required for resin compositions used as a sealing material for ICs and the like include (1) a low melt viscosity sufficient for the resin composition to be molded without cutting or deforming bonding wires for elements and (2) a coefficient of linear expansion close to metals. The coefficient of linear expansion has conventionally been adjusted by the addition of a large amount of fillers. The fillers, however, can be added to the resin composition only with decrease in the mechanical strength.
Because of this, thermoset resins, such as epoxy resins and silicone resins, have been used heretofore. However, because the thermoset resins can be manufactured only with a low productivity, spur runners of thermoset resins cannot be reused, and thermoset resins cannot be easily recycled, a great attention has been given to thermoplastic resins. Among thermoplastic resins, polyarylene sulfide (PAS) and polyphenylene sulfide (PPS) are considered to be particularly promising sealing materials due to their superior heat resistant and flame retarding characteristics.
The following compositions have been proposed as the composition using the PAS.
(1) A composition with a silane coupling agent added to improve the characteristics (Japanese Patent Publication (kokoku) No. 18351/1993). PA1 (2) A composition with an olefin copolymer made from .alpha.olefin and .alpha., .beta.-unsaturated glycidyl ester added to PAS (Japanese Patent Application Laid-open (kokai) Nos. 17594/1988 and 68101/1991). PA1 (3) A composition with an ethylenic copolymer elastomer added to an aminated PPS (Japanese Patent Application Laid-open (kokai) No. 153262/1992). PA1 (4) A composition comprising PPS, an ethylenic terpolymeric elastomer, and a silane coupling agent (Japanese Patent Application Laid-open (kokai) No. 202245/1993). PA1 (A) a polyarylene sulfide resin, PA1 (B) silica, PA1 (C) (cl) a terpolymeric elastomer made from ethylene, an .alpha., .beta.-unsaturated carboxylate, and maleic acid anhydride and/or (c2) a graft composite elastomer which is a vinyl monomer grafted composite elastomer of polyorganosiloxane and alkyl (meth)acrylate, and PA1 (D) a mercaptosilane coupling agent, and wherein the amounts of components (A), (B), (C) and (D) satisfy the following inequalities (I) to (IV), EQU 0.15.ltoreq.A/(A+B+C).ltoreq.0.60 (I), EQU 0.40.ltoreq.B/(A+B+C).ltoreq.0.85 (II), EQU 0.03.ltoreq.C/A.ltoreq.0.30 (III), EQU and EQU 0.001.ltoreq.D/(A+B+C).ltoreq.0.05 (IV).
The composition (1) exhibits only insufficient improvement in the toughness and fluidity. A large amount of the hydrogenated SBS must be added to the composition (2), giving rise to poor heat resistance and chemical resistance. The composition (3) has poor fluidity because of the large molecular weight of the PPS and is thus not suitable as a sealing material. The composition (4) was invented in order to improve the mechanical strength of PPS without regard to the viscosity, of which the reduction is important for a composition used as a sealing material. The silane coupling agents disclosed accompany an increase in the viscosity and are not desirable. These compounds are therefore not necessarily satisfactory.
The present invention was accomplished in view of this situation and has an object of providing a polyarylene sulfide resin composition which exhibits superior mechanical strength and high fluidity and can be used effectively for sealing ICs and various electronic parts.